Tissue culture methods are being employed to determine, by comparing in vivo and in vitro alterations produced in embryonic systems by some selected chemical teratogens, the initial sites of effect involved in teratogenesis. Morphologic and metabolic alterations produced in cell proliferation, epithelial-mesenchymal interaction, and the process of cell differentiation in the initiation of chondrogenesis are under investigation as encountered in the origin of congenital malformations of orofacial and limb development. The chemical agents employed in this study are: a) those which are known to induce a high incidence of these malformations in experimental animals or man, e.g. retinoic acid (vitamin A acid), 6-aminonicotinamide and thalidomide, b) those which are known also to be active in cancer chemotherapy through their effect on nucleic acid metabolism, such as aminopterin, 6-diazo-5- oxo-norleucine (DON) on 5-bromodeoxyuridine, and c) those which participate in the metabolism of the intercellular materials of connective tissue and cartilage (glycosaminoglycans and collagen), such as azetidine-2-carboxylic acid, DON and azaserine. Whole mounts and routine histologic and histochemical methods will be employed for morphologic study. Radioautography, radiochemical procedures, microfractionation, and electrophoretic analyses will be used for quantitative studies on the biosynthesis of: general proteins, collagen, glycosaminoglycans, and DNA. Specific alterations in the cytoplasmic organelles of cells responsible for the synthesis of these products as well as the architecture of the extracellular matrix will be investigated with the electron microscope.